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<h1>
<span class="m-breadcrumb"><a href="cudaFlowAlgorithms.html">cudaFlow Algorithms</a> »</span>
Parallel Merge
</h1>
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<h3>Contents</h3>
<ul>
<li><a href="#CUDAParallelMergeIncludeTheHeader">Include the Header</a></li>
<li><a href="#cudaFlowMergeTwoRangesOfItems">Merge two Sorted Ranges of Items</a></li>
<li><a href="#cudaFlowMergeTwoRangesOfKeyValueItems">Merge two Sorted Ranges of Key-Value Items</a></li>
<li><a href="#cudaFlowMergeMiscellaneousItems">Miscellaneous Items</a></li>
</ul>
</div>
<p>cudaFlow provides template methods to create parallel merge tasks on a CUDA GPU.</p><section id="CUDAParallelMergeIncludeTheHeader"><h2><a href="#CUDAParallelMergeIncludeTheHeader">Include the Header</a></h2><p>You need to include the header file, <code>taskflow/cuda/algorithm/merge.hpp</code>, for creating a parallel-merge task.</p></section><section id="cudaFlowMergeTwoRangesOfItems"><h2><a href="#cudaFlowMergeTwoRangesOfItems">Merge two Sorted Ranges of Items</a></h2><p><a href="classtf_1_1cudaFlow.html#af8fa5d69a57d010d7a3ee2756d85859c" class="m-doc">tf::<wbr />cudaFlow::<wbr />merge</a> performs a parallel merge over two ranges of elements into a sorted range of items. The following code merges two sorted arrays <code>input_1</code> and <code>input_2</code>, each of 1000 items, into a sorted array <code>output</code> of 2000 items.</p><pre class="m-code"><span class="k">const</span> <span class="kt">size_t</span> <span class="n">N</span> <span class="o">=</span> <span class="mi">1000</span><span class="p">;</span>
<span class="kt">int</span><span class="o">*</span> <span class="n">input_1</span> <span class="o">=</span> <span class="n">tf</span><span class="o">::</span><span class="n">cuda_malloc_shared</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="n">N</span><span class="p">);</span> <span class="c1">// input vector 1</span>
<span class="kt">int</span><span class="o">*</span> <span class="n">input_2</span> <span class="o">=</span> <span class="n">tf</span><span class="o">::</span><span class="n">cuda_malloc_shared</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="n">N</span><span class="p">);</span> <span class="c1">// input vector 2</span>
<span class="kt">int</span><span class="o">*</span> <span class="n">output</span> <span class="o">=</span> <span class="n">tf</span><span class="o">::</span><span class="n">cuda_malloc_shared</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="mi">2</span><span class="o">*</span><span class="n">N</span><span class="p">);</span> <span class="c1">// output vector</span>
<span class="c1">// initializes the data</span>
<span class="k">for</span><span class="p">(</span><span class="kt">size_t</span> <span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span> <span class="n">i</span><span class="o"><</span><span class="n">N</span><span class="p">;</span> <span class="n">i</span><span class="o">++</span><span class="p">)</span> <span class="p">{</span>
<span class="n">input_1</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">=</span> <span class="n">rand</span><span class="p">()</span><span class="o">%</span><span class="mi">100</span><span class="p">;</span>
<span class="n">input_2</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">=</span> <span class="n">rand</span><span class="p">()</span><span class="o">%</span><span class="mi">100</span><span class="p">;</span>
<span class="p">}</span>
<span class="n">std</span><span class="o">::</span><span class="n">sort</span><span class="p">(</span><span class="n">input_1</span><span class="p">,</span> <span class="n">input1</span> <span class="o">+</span> <span class="n">N</span><span class="p">);</span>
<span class="n">std</span><span class="o">::</span><span class="n">sort</span><span class="p">(</span><span class="n">input_2</span><span class="p">,</span> <span class="n">input2</span> <span class="o">+</span> <span class="n">N</span><span class="p">);</span>
<span class="c1">// merge input_1 and input_2 to output</span>
<span class="n">tf</span><span class="o">::</span><span class="n">cudaFlow</span> <span class="n">cf</span><span class="p">;</span>
<span class="n">tf</span><span class="o">::</span><span class="n">cudaTask</span> <span class="n">task</span> <span class="o">=</span> <span class="n">cf</span><span class="p">.</span><span class="n">merge</span><span class="p">(</span>
<span class="n">input_1</span><span class="p">,</span> <span class="n">input_1</span> <span class="o">+</span> <span class="n">N</span><span class="p">,</span> <span class="n">input_2</span><span class="p">,</span> <span class="n">input_2</span> <span class="o">+</span> <span class="n">N</span><span class="p">,</span> <span class="n">output</span><span class="p">,</span>
<span class="p">[]</span><span class="n">__device__</span> <span class="p">(</span><span class="kt">int</span> <span class="n">a</span><span class="p">,</span> <span class="kt">int</span> <span class="n">b</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="n">a</span> <span class="o"><</span> <span class="n">b</span><span class="p">;</span> <span class="p">}</span> <span class="c1">// comparator</span>
<span class="p">);</span>
<span class="n">cf</span><span class="p">.</span><span class="n">offload</span><span class="p">();</span></pre></section><section id="cudaFlowMergeTwoRangesOfKeyValueItems"><h2><a href="#cudaFlowMergeTwoRangesOfKeyValueItems">Merge two Sorted Ranges of Key-Value Items</a></h2><p><a href="classtf_1_1cudaFlow.html#a9cdfde0bafee035c0075619d386a9a43" class="m-doc">tf::<wbr />cudaFlow::<wbr />merge_by_key</a> performs key-value merge over two sorted ranges in a similar way to <a href="namespacetf.html#a37ec481149c2f01669353033d75ed72a" class="m-doc">tf::<wbr />cuda_merge</a>; additionally, it copies elements from the two ranges of values associated with two input keys, respectively. The following code performs key-value merge over <code>a</code> and <code>b:</code></p><pre class="m-code"><span class="k">const</span> <span class="kt">size_t</span> <span class="n">N</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span>
<span class="kt">int</span><span class="o">*</span> <span class="n">a_keys</span> <span class="o">=</span> <span class="n">tf</span><span class="o">::</span><span class="n">cuda_malloc_shared</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="n">N</span><span class="p">);</span>
<span class="kt">int</span><span class="o">*</span> <span class="n">a_vals</span> <span class="o">=</span> <span class="n">tf</span><span class="o">::</span><span class="n">cuda_malloc_shared</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="n">N</span><span class="p">);</span>
<span class="kt">int</span><span class="o">*</span> <span class="n">b_keys</span> <span class="o">=</span> <span class="n">tf</span><span class="o">::</span><span class="n">cuda_malloc_shared</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="n">N</span><span class="p">);</span>
<span class="kt">int</span><span class="o">*</span> <span class="n">b_vals</span> <span class="o">=</span> <span class="n">tf</span><span class="o">::</span><span class="n">cuda_malloc_shared</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="n">N</span><span class="p">);</span>
<span class="kt">int</span><span class="o">*</span> <span class="n">c_keys</span> <span class="o">=</span> <span class="n">tf</span><span class="o">::</span><span class="n">cuda_malloc_shared</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="mi">2</span><span class="o">*</span><span class="n">N</span><span class="p">);</span>
<span class="kt">int</span><span class="o">*</span> <span class="n">c_vals</span> <span class="o">=</span> <span class="n">tf</span><span class="o">::</span><span class="n">cuda_malloc_shared</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="mi">2</span><span class="o">*</span><span class="n">N</span><span class="p">);</span>
<span class="c1">// initializes the data</span>
<span class="n">a_keys</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="mi">8</span><span class="p">,</span> <span class="n">a_keys</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span>
<span class="n">a_vals</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="mi">1</span><span class="p">,</span> <span class="n">a_vals</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span>
<span class="n">b_keys</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="mi">3</span><span class="p">,</span> <span class="n">b_keys</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="o">=</span> <span class="mi">7</span><span class="p">;</span>
<span class="n">b_vals</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="mi">3</span><span class="p">,</span> <span class="n">b_vals</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="o">=</span> <span class="mi">4</span><span class="p">;</span>
<span class="c1">// performs key-value merge</span>
<span class="n">tf</span><span class="o">::</span><span class="n">cudaFlow</span> <span class="n">cf</span><span class="p">;</span>
<span class="n">cf</span><span class="p">.</span><span class="n">merge_by_key</span><span class="p">(</span>
<span class="n">a_keys</span><span class="p">,</span> <span class="n">a_keys</span><span class="o">+</span><span class="n">N</span><span class="p">,</span> <span class="n">a_vals</span><span class="p">,</span>
<span class="n">b_keys</span><span class="p">,</span> <span class="n">b_keys</span><span class="o">+</span><span class="n">N</span><span class="p">,</span> <span class="n">b_vals</span><span class="p">,</span>
<span class="n">c_keys</span><span class="p">,</span> <span class="n">c_vals</span><span class="p">,</span>
<span class="p">[]</span> <span class="n">__device__</span> <span class="p">(</span><span class="kt">int</span> <span class="n">a</span><span class="p">,</span> <span class="kt">int</span> <span class="n">b</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="n">a</span> <span class="o"><</span> <span class="n">b</span><span class="p">;</span> <span class="p">},</span>
<span class="p">);</span>
<span class="n">cf</span><span class="p">.</span><span class="n">offload</span><span class="p">();</span>
<span class="c1">// now, c_keys = {1, 3, 7, 8}</span>
<span class="c1">// now, c_vals = {2, 3, 4, 1}</span>
<span class="c1">// delete the device memory</span>
<span class="n">tf</span><span class="o">::</span><span class="n">cuda_free</span><span class="p">(</span><span class="n">buffer</span><span class="p">);</span>
<span class="n">tf</span><span class="o">::</span><span class="n">cuda_free</span><span class="p">(</span><span class="n">a_keys</span><span class="p">);</span>
<span class="n">tf</span><span class="o">::</span><span class="n">cuda_free</span><span class="p">(</span><span class="n">b_keys</span><span class="p">);</span>
<span class="n">tf</span><span class="o">::</span><span class="n">cuda_free</span><span class="p">(</span><span class="n">c_keys</span><span class="p">);</span>
<span class="n">tf</span><span class="o">::</span><span class="n">cuda_free</span><span class="p">(</span><span class="n">a_vals</span><span class="p">);</span>
<span class="n">tf</span><span class="o">::</span><span class="n">cuda_free</span><span class="p">(</span><span class="n">b_vals</span><span class="p">);</span>
<span class="n">tf</span><span class="o">::</span><span class="n">cuda_free</span><span class="p">(</span><span class="n">c_vals</span><span class="p">);</span></pre></section><section id="cudaFlowMergeMiscellaneousItems"><h2><a href="#cudaFlowMergeMiscellaneousItems">Miscellaneous Items</a></h2><p>Parallel merge algorithms are also available in <a href="classtf_1_1cudaFlowCapturer.html" class="m-doc">tf::<wbr />cudaFlowCapturer</a> with the same API.</p></section>
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